Emulsions make it possible to simultaneously convey water-soluble and fat-soluble substances and thus find an application in particular in the cosmetics, pharmaceutical and veterinary fields and in the field of detergents.
In the cosmetics field, there exists a requirement on the part of the user of products in the form of emulsions to have available emulsions which exhibit appropriate sensory characteristics. Emulsions which provide a feeling of freshness and which are felt to be non-“sticky” when applied to the skin are particularly desired.
Emulsions are categorized according to the nature of the continuous phase (also referred to as “external phase”) in which droplets of the other phase (referred to as “internal phase”) are dispersed.
In the case where the oil droplets are dispersed in an aqueous continuous phase, the system is called an emulsion of “oil-in-water” (O/W) type.
In the case where the water droplets are dispersed in an oily continuous phase, the emulsion is of “water-in-oil” (W/O) type.
Generally, among these two types of emulsions, it is easier to manufacture emulsions of oil-in-water (O/W) type as emulsions of W/O type are intrinsically unstable thermodynamically. This is because, if equal amounts of water and of oil are mixed, the formation of an emulsion with an aqueous continuous phase is always observed as the cohesive forces between water molecules are stronger than those between oil molecules.
Nevertheless, emulsions with an oily continuous phase (W/O) exhibit numerous advantages:                the separation between the water droplets reduces the possibility of growth of microorganisms. The use of antiseptics, essential when the continuous phase is aqueous, may be avoided;        they keep well at low temperature, being much less sensitive in this respect than emulsions of O/W type;        the oily continuous phase covers the skin and protects it from dehydration and from external substances.        
In the development of an emulsion system with an oily continuous phase, two types of modifications have been envisaged:                modifications of a mechanical nature regarding the combining of the phases (order of addition of the phases, control of the flow rate during the combining of the phases, temperature of the phases, rate of stirring, and the like);        modifications with regard to the chemical constituents having the result of stabilizing the emulsion.        
As regards the modifications of a mechanical nature, the operating procedures employed for preparing W/O emulsions generally require:                a) a high energy input in the form of thermal activation (the aqueous and fatty phases are typically heated to 80° C.), which sometimes has to be followed by well-controlled gradual cooling; and/or        b) the creation of turbulence in the two-phase medium to be emulsified (high rate of stirring (thousands of revolutions per minute) and high shear brought about by specific geometries of the stirrers).        
As regards the modifications of a chemical nature, mention may be made of:                a) the use of microcrystalline waxes, such as ozokerite, which absorb the oil and prevent it from being exuded;        b) the use of liquid paraffins as fatty phase as these paraffins are easier to emulsify;        c) the addition of inorganic salts, such as, in particular, sodium chloride or magnesium chloride, making it possible to increase the cohesion of the interfacial film.        
U.S. Pat. No. 5,746,945 discloses emulsions of water-in-oil type which are stabilized by an emulsifying system having two components: a) a polysiloxane/polyalkyl/polyether copolymer, and b) a phthalic anhydride derivative (a monoamide). The method of preparation of emulsions in this document consists of the gradual addition of the aqueous phase to the oily phase. The two phases are heated, each independently of the other, to 160 to 165° F. (71 to 74° C.) before being combined to produce the emulsion.
The document WO 97/40814 discloses W/O emulsions intended in particular to be used to impregnate baby wipes. The organic phase of the emulsions necessarily comprises a wax. The emulsifiers used are of carboxylic acid type, which are substituted by hydrocarbons, or ABA block copolymers, involving monomers such as 12-hydroxystearic acid and ethylene glycol, or an alkyl dimethicone copolyol. As regards the process used to prepare the emulsions, the fatty phase and the aqueous phase are typically heated to 160° F. (71° C.) and then they are mixed at this temperature to produce the emulsion.
The typical procedures of the prior art thus exhibit a number of disadvantages related in particular to the need to provide a significant energy input to produce the emulsion.
One problem to be solved thus consists in providing W/O emulsions with a high content of aqueous phase which exhibit in particular a fresh and nonsticky texture.
Another problem to be solved consists in making available a process for the preparation of such emulsions which is:                simple, that is to say that the number of stages employed is reduced and that factors such as the exact control of the flow rates for introducing the phases are not critical for the satisfactory operation of the process, and        economical, that is to say that it is not necessary to expend a great deal of energy, either in heating the phases to be combined or in the vigorous stirring to be provided during the preparation of the emulsion.        